Yet more fun with squamate phylogeny

[David Marjanovic <david.marjanovic@gmx.at>]

John D. Scanlon: Skull of the large non-macrostomatan snake *Yurlunggur* 
from the Australian Oligo-Miocene, Nature 439, 839 -- 842 (16 February 2006)

Abstract (refs removed):
"Understanding the origin and early evolution of snakes from lizards depends 
on accurate morphological knowledge of the skull in basal lineages, but 
fossil specimens of archaic snakes have been rare, and either fragmentary or 
difficult to study as a result of compression by enclosing sediments. A 
number of Cenozoic fossil snakes from Australia have vertebral morphology 
diagnostic of an extinct group, Madtsoiidae, that was widespread in Gondwana 
from mid-Cretaceous (Cenomanian) to Eocene times, and also reached Europe in 
the late Cretaceous period. Despite this long history, only about half the 
skull is known from the best-known species *Wonambi naracoortensis*, and the 
few known cranial elements of other species have added little further 
evidence for phylogenetic relationships. Conflicting hypotheses have been 
proposed for their relationships and evolutionary significance, either as 
basal ophidians with many ancestral (varanoid- or mosasaur-like) features, 
or advanced (macrostomatan) alethinophidians of little relevance to snake 
origins. Here I report two partial skeletons referred to *Yurlunggur*, from 
the late Oligocene and early Miocene of northern Australia, which together 
represent almost the complete skull and mandible. The exceptionally 
preserved skulls provide new evidence linking *Yurlunggur* with *Wonambi* 
and other madtsoiids, falsifying predictions of the macrostomatan 
hypothesis, and supporting the exclusion of Madtsoiidae from the clade 
including all extant snakes."

In total practically the complete skull is now known -- and full of 
plesiomorphies, many of them relating to limited (but not absent) kinesis. 
The teeth look like a boa's. Riversleigh fossils are preserved in 3D, 
usually undistorted, and can be acid-prepared, as the specimens mentioned 
here were.

*Yurlunggur* and *Wonambi* each have a few different convergences on 
Macrostomata!

Madtsoiidae is mentioned to be "presumed to be constrictors ecologically 
analogous to living pythons and boas", followed by a long string of 
references. Don't ask me why they co-occurred with pythons, then...

Bremer decay index left, bootstrap support right:

--+--composite "varanoid" outgroup
 `--+--*Pachyrhachis*
    `--3,86--*Haasiophis*
          `--3,67--4,82--*Yurlunggur*
                |       `--*Wonambi*
                `--5,72--*Dinilysia*
                     `--11,98--34,100,Scolecophidia (3 OTUs)
                           `--3,62--3,48,Anilioidea (4 OTUs)
                                `--14,99,Macrostomata (10 OTUs)

The last three lines are the ophidian crown-group (Serpentes), the last two 
are called Alethinophidia. The character matrix comes from Lee & Scanlon 
2002 (abstract: 
http://www.journals.cambridge.org/action/displayAbstract?fromPage=online&aid=120939).